Yet many of the men I know who have been with the same woman for 50 or 60 years, when both of them are in their 80s, still seem to love them."

How many old men fall in love with 80 year old women?

There should be plenty of 80 year old widowers, and plenty of 80 year old widows available.
How many 80 year old widowers fall in love, sexually, with 80 year old women they were not previously familiar with?